Dynorphin-containing pathways in the substantia nigra and ventral tegmentum: A double labeling study using combined immunofluorescence and retrograde tracing

Abstract

A rich plexus of dynorphin (DYN)-containing fibers and terminals is present throughout the substantia nigra-ventral tegmental area (SN-VTA). Lesion studies have indicated that these terminals originate, in part, from DYN-containing cell bodies in the caudate-putamen. We have utilized combined immunofluorescence and retrograde tracing techniques to confirm this finding and to demonstrate the presence of other potential DYN pathways in the region of SN-VTA. The location of DYN-containing cell bodies and fibers was determined by immunohistochemistry in untreated and colchicine-treated adult albino rats. In further double-labeling experiments, animals received injections of fluorescent retrograde tracers into SN-VTA, brainstem or amygdala, followed one to fourteen days later by colchicine treatment. Brains were subsequently processed for combined FITC immunofluorescence and fluorescent dye localization. These experiments provided neuroanatomical evidence for heterogeneous DYN-containing pathways in the SN-VTA. Topographically organized afferents arose from the caudate putamen, amygdala and hypothalamus, while efferents arose from only the most lateral sectors of the SN to the amygdala. While most of the observed descending projections terminated in the SN-VTA, hypothalamic and amygdala projections also continued en passage to the brainstem. These findings implicate DYN systems in striatal and limbic, as well as neuroendocrine, functions.